A lamp is an energy converter. Although it may carry out secondary functions, its prime purpose is the transformation of electrical energy into visible electromagnetic radiation. There are various types of lamps that are available in the market namely incandescent lamp, high intensity discharge lamp, tungsten halogen lamps, tubular fluorescent lamps, compact fluorescent lamps, induction lamps, mercury lamps, metal halide lamps, sodium lamps and many more.
A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamps that produce light by means of an electric arc, which is between tungsten electrodes that are in-turn housed inside a translucent or transparent fused quartz or fused alumina arc tube. These lamps require ballast. The ballast is a device intended to limit the amount of current in an electric circuit. For example, inductive ballast is used in fluorescent lamps, to limit the current through the tube.
These lamps are designed under the American National Standards Institute (“ANSI”) standard. ANSI standard describes the essential design features and operating characteristics of reference ballasts for fluorescent and other lamps.
The traditional ballasts function as constant current sources. Many lamps use such ballasts to maintain the input current. The retrofit lamps seek to consume less power, thus they typically function at the same current and a lower voltage than the legacy lamps they are replacing. This generally works well with actual ballasts in the field. However, ANSI ballast test defines a thevenin equivalent circuit that is equivalent to ballasts. Thus, when a low voltage lamp, like retrofit lamp, is provided to the ANSI reference thevenin equivalent ballast, it increases the input current that in-turn violates the Underwriters Laboratories (UL) ANSI Ballast requirement.
The prior art technologies fail to disclose the design circuits for the LED lamps that are satisfying the operational characteristics as per UL ANSI standards. Further, none of the prior art technologies teach about maintaining the compatibility of the retrofit LED lamps with the ballasts present in the market to replace fluorescent or HID lamps.
Furthermore, there are several problems with traditional lamp circuits. When a low voltage lamp is presented to ANSI reference ballast, it increases the current, hence violates the UL requirement. Similarly, power consumption is more in the traditional lamps.
Also, when a traditional approach of adding a capacitive coupling between the retrofit lamp and ballast to add a reactive component to the lamp impedance and throttle back current is implemented, the approach does not work during compatibility testing for two reasons: the difference in power level that a compatible compact florescent lamp (“CFL”) LED lamp is seeking to bridge (50%) is larger than what is typically bridged in HID or linear fluorescent or other lamps (20-30%). This further requires a smaller capacitance that introduces a much larger reactive component to the lamp impedance. This larger reactance creates compatibility issues with ballasts that operation at lower frequencies and its impedance is higher and thus causes the ballast to turn off after hitting its over voltage protection limit or other protection circuitry.
Further, the CFL ballasts last longer than T8 ballasts and thus the age and variety of ballasts that the LED lamp needs to support is much larger than what is required by T8 lamps. Therefore, high compatibility cannot be achieved with a simple reactive circuit.
Presently, Cree has designed and manufactured a T8 (tubular 1-inch diameter) LED fluorescent replacement lamp. In this lamp, LEDs strings with plurality of LEDs are arranged in parallel. The circuits for the components on each end of the lamp are shown in FIGS. 1A and 1B. 102 and 104 are test points on a PC board. FIG. 1A shows the circuit that connects the parallel strings of LEDs through a resistor R1. Points 106 and 108 are the shorted returns on the ballast. FIG. 1B shows the circuit for the Inductor L1/resistor R2 section. Points 202 and 204 are power from the ballast. 102 and 104 are printed circuit board (“PCB”) rest points. Dimming fluorescent ballasts keep the same voltage across the lamps but lowers the current that works out well for LED lights since LEDs are current-controlled components. However, the ballasts are constant current sources.
Hence, there exists a need to design and develop a retrofit LED lamp with an electrical circuit that may increase the compatibility of the lamps with the existing ballasts, when such lamps replace the available fluorescent lamps or HID lamps, with a constant voltage source ballast. Also, there is a need to imply constant voltage source ANSI reference ballast with the retrofit LED lamps. Further, this also creates a need to reduce the power consumption during the operation of the lamps.